SL-16436 and SL-16327 Fix for RenderDebugGL test failures and fix for grey textures

indra/llrender/llgl.cpp

indra/llrender/llimagegl.cpp

indra/llrender/llimagegl.h

indra/llrender/llrender.cpp

indra/newview/CMakeLists.txt

..._settings/shaders/class1/deferred/avatarAlphaShadowF.glsl

..._settings/shaders/class1/deferred/avatarAlphaShadowV.glsl

indra/newview/lldrawable.h

indra/newview/lldrawpooltree.cpp

indra/newview/llface.h

indra/newview/llglsandbox.cpp

indra/newview/llspatialpartition.cpp

indra/newview/llspatialpartition.h

indra/newview/lltextureatlas.cpp

indra/newview/lltextureatlas.h

indra/newview/lltextureatlasmanager.cpp

indra/newview/lltextureatlasmanager.h

indra/newview/llviewertexture.cpp

indra/newview/llvovolume.cpp

indra/newview/pipeline.cpp